Biotechnological approaches to fight fruit flies of agricultural importance

Abstract

Tephritid fruit flies destroy fruits and vegetables, causing tremendous economic losses and bringing a barrier to trade in fruits, vegetables and their associated products. The Sterile Insect Technique (SIT), a target-specific and environment-friendly pest control method, has been used to combat several insect pests for over five decades and has proven to be quite effective against tephritids. Basically, SIT requires mass-production and mass-release of sterile insects to reduce the wild population of the same species. Sex separation prior to release is important in SIT for many insects as male-only release has been shown to achieve a more effective population control. Post release, the wild population and their released sterile counterparts need to be effectively monitored to ascertain the success of the programme. While SIT has achieved great success, improvements to the various technical aspects are constantly made as that will shape the method into a highly efficient, safer and cheaper programme to execute. Biotechnology has a great potential to bring desired improvements to SIT in ways that may be difficult to achieve by other means. This study aimed at an improvement of SIT using molecular biotechnological approaches. An early-acting sex separation system based on female-specific embryonic lethality was developed as a transgenic sex separation alternative for SIT in the Mediterranean fruit fly Ceratitis capitata using a sex-specifically spliced intron in a proapoptotic gene driven by a conditional heterologous transactivator under the control of a blastoderm-specific promoter. Transgene modification by site-specific recombination in the sexing effector line was further performed and subsequent stabilization of the transgene by transposase-induced partial removal of transposon inverted terminal repeat (ITR) achieved to make the line safer for application in operational SIT programmes. The strategy used for transgene stabilization also provides an avenue to combine other transgenic systems with the early-acting sexing system and to improve the efficiency of this site-specific recombination strategy in medfly, the upstream region of the maternal-effect and primordial germ cell gene nanos was isolated following characterization of the gene. The regulatory elements of this gene will be highly beneficial in constructing a more efficient site-specific recombination system, which should make it easier to achieve various desired transgenic system combinations and generate composite strains of medfly for a better SIT.